As is well known, superconducting magnet apparatuses are used in various fields. Generally known superconducting magnet apparatus is adapted so that superconducting wires are wound like a coil and is then dipped into liquid helium, which is contained in a refrigerant container and serves as a refrigerant for cooling superconducting materials, to thereby generate a magnetic flux, namely, a magnetic field in a previously set space, as disclosed in Japanese Unexamined Patent Publication No. 4-49948.
FIG. 68 illustrates an example of such a superconducting magnet apparatus. In a refrigerant container 11, a static-magnetic-field generating source 13 consisting of superconducting wire wound around a support 14 like coils is placed. Wire made of Nb3Sn or NbTi is used as the superconducting wire. Magnetic field generated by the aforesaid static-magnetic-field generating source 13 is formed in a static-magnetic-field space 18 along the central axis 19 thereof. Incidentally, the static-magnetic-field generating source 13 composed of a plurality of coils. Further, the magnetic filed formed in the static-magnetic-field-space 18 can be regulated by changing the number of turns of each of the coils. Moreover, a refrigerant, such as liquid helium, 12 for cooling superconducting materials is output from a refrigerant source 17 and is injected from a refrigerant injecting port 15 through cock 16 into the refrigerant container 11. Further, a magnetizing electric current to be supplied to the coils of the aforesaid static-magnetic-field generating source 13 is introduced thereto through a connector portion 21 and a persistent current circuit switch circuit 24 from an exciting power supply 20. The aforementioned persistent current circuit switch 24 is used when operating the static-magnetic-field generating source 13 in a persistent current mode. FIG. 69 shows an example of the persistent current circuit switch 24. Namely, the persistent current switch 24 is contained in the refrigerant container 11 together with the static- magnetic-field generating source 13 and is cooled by using the refrigerant 12 for cooling superconducting materials. Further, the aforesaid persistent current circuit switch 24 is obtained by winding a superconducting wire 28 together with a heater wire 29 like coils and by heat-insulating the wires by epoxy resin or the like. Superconducting wire made by using CuNi alloy as a base metal material is used as this superconducting wire 28. Further, a manganin heater wire is usually used as the heater wire 29. Static-magnetic-field generating source 13 is connected with the superconducting wire 28 and the exciting power supply 20 at persistent current joints P and Q, respectively. The switch 26 is provided at the side of the exciting power supply 20. The heater wire 29 is connected with a heater power supply 22 through a connector portion 23 (see FIG. 68), and a switch 27 is provided at the side of the heater power supply 22. When the heater wire 29 is heated, the temperature of the superconducting wire 28 becomes equal to or higher than a critical temperature Tc and thus the persistent current circuit switch 24 is brought into OFF-state. In contrast, when the heater wire 29 is not heated, the superconducting wire 28 is in a superconducting state, and thus the persistent current circuit switch 24 is put into ON-state.
To operate the static-magnetic-field generating source 13 in the persistent current mode, the following steps are performed.
(1) The static-magnetic-field generating source 13 and the persistent current circuit switch 24 are cooled by using the refrigerant 12 for cooling superconducting materials, and are put into the superconducting state.
(2) The switch 27 provided at the side of the heater power supply 22 is then turned on, so that the persistent current circuit switch 24 is put into OFF-state. Moreover, the switch 26 provided at the side of the exciting power supply 20 is turned on, so that the static-magnetic-field generating source 13 is excited by means of the exciting power supply 20 by applying electric current, so as to reach a rated current.
(3) Subsequently, the switch 27 provided at the side of the heater power supply 22 is turned off to thereby stop heating the heater wire. Thus, the superconducting wire 28 of the persistent current circuit switch 24 is brought into a conducting state (namely, ON-state). Moreover, the current flowing from the exciting power supply is decreased to 0. At that time, the electric current flowing through the superconducting wire 28 of the persistent current circuit switch 24 is raised to the rated current value of the static-magnetic-field generating source 13. In this state, the exciting power supply 20 can be detached from the apparatus.
However, the conventional superconducting magnet apparatus has the following problems, owing to the facts that the superconducting coil is used in the static-magnetic-field generating source 13 and that the persistent current circuit switch 24 is used to operate the apparatus in the persistent current mode.
(1) Magnetic flux decreases with time, owing to the resistance of the connecting portion of the superconducting coil.
(2) Principal factor in generating a quench are caused due to the contact potential difference occurring in the joint portion between CuNi alloy of the persistent current circuit switch 24 and Cu of the superconducting wire 28.
(3) Energizing current is reduced owing to disarray in the magnitude and direction of a magnetic field occurring in the connecting portion of the superconducting coil.
(4) Partial mechanical change in the coil due to wrong conditions of fixation of the coil results in local generation of heat. Further, the local generation of heat is promoted by a change in the state of a portion, in which heat is locally generated, of the coil from the normal conducting state to the superconducting state thereof. Thus, a principal factor in generating a quench is caused.
(5) Large part of principal steps of an operation of manufacturing a superconducting coil and a coil connecting operation and a coil holding operation have no choice but to be manually performed. Thus, it is difficult to obtain uniform manufacturing accuracy. Moreover, skilled workers are necessary for manufacturing superconducting magnet apparatuses with sufficiently high precision.
Thus, the present invention is accomplished to deal with such problems of the conventional apparatus. Accordingly, the present invention aims at providing a small-sized high-precision superconducting magnet apparatus which can prevent an occurrence of the principal factor in generating a quench and can restrain the magnetic flux from varying with time, and at providing a method of regulating the magnetization of such a superconducting magnet apparatus, by which the superconducting magnet apparatus can be uniformly magnetized.